Lymphocyte muscarinic receptors and platelet monoamine oxidase-B as biomarkers of CNS function: effects of age and gender in healthy humans

Lymphocyte cholinergic muscarinic receptors (MRs) and platelet monoamine oxidase-B (MAO-B) activity are considered surrogate markers of the same parameters in the central nervous system. Lymphocyte MR binding and platelet MAO-B activity were measured in a consistent number of healthy human adults and analysed according to gender and age. The mean value ± S.D. of MR binding neither differed between males (12.2 ± 10.0 fmol/106 cells, range: 0.5-37.9, n = 86) and females (10.7 ± 9.7 fmol/106 cells, range: 0.5-39.7, n = 69) nor among age groups. MAO-B activity was significantly higher in women (geometric mean: 11.3 nmol/mg protein/h, with 65% of values from 7.3 to 17.6; n = 43), than in men (7.7 nmol/mg protein/h, with 65% of values from 4.5 to 13; n = 95). Males aged 56-66 years displayed a higher, though not statistically significant, basal enzyme activity than younger subjects. Altogether these data indicate gender-related differences in MAO activity, but not in MR binding, and inter-individual differences in the basal values of both peripheral blood markers in healthy subjects.